(1) Field of the Invention
The instant invention relates to acoustic damping of rigid plates and more particularly to a mass-loaded coating for reducing the resonant frequency of a ceramic disc in an acoustic transducer.
(2) Description of the Prior Art
Acoustic transducers have heretofore been known in the art. In this connection, an acoustic transducer of the general type contemplated herein is described in detail in the technical memorandum "Modification (XU1643U) of the XU1643 Transducer", Naval Underwater Systems Center, New London Laboratory (1984). The XU1643U transducer includes three ceramic bimorph discs which are assembled in a mounting fixture referred to as a triple lollipop projector. Each of the ceramic bimorphs is individually encapsulated in polyurethane, and each has a slightly different resonant frequency. In order for the projector to function properly, all three ceramic bimorphs must be acoustically matched so that they all have nearly the same resonant frequency. One known method of acoustic matching is mass-loading the bimorphs whose resonant frequency is too high, i.e., the process of adding mass to an object to dampen the resonant frequency thereof. Conventional mass-loading techniques comprise affixing prefabricated damping elements, such as tiles or weights, to an object to add mass to the object, however, the ceramic transducer discs pose a special problem in that the ceramic discs are mounted in very close proximity, and the conventional damping elements do not fit within the predetermined size constraints of the mounting fixture. It has thus been found that these ceramic transducer elements do not readily lend themselves to conventional mass-loading techniques.